Chinook Salmon Fry Research Articles

Using parentage-based tagging to estimate survival of Chinook salmon fry in a large storage reservoir

Using parentage-based tagging to estimate survival of Chinook salmon fry in a large storage reservoir

A correlation between seasonally changing photoperiod, whole body lipid, and condition factor in juvenile spring Chinook salmon (Oncorhynchus tshawytscha).

The regulation of lipid stores is a central process for the physiology and ecology of fishes. Seasonal variation in lipid stores has been directly linked to survival of fishes across periods of food deprivation. We assessed whether a seasonally changing photoperiod was correlated to seasonal changes in energetic status to help better understand these important processes. Groups of first feeding Chinook salmon fry were introduced to a seasonal photoperiod cycle, but the point of entrance into the seasonal cycle varied from near the winter solstice (December), to either side of the spring equinox (February & May). Temperature and feeding rate were similar for all treatments. Subsequently, condition factor and whole body lipid content were assessed through a seasonal progression. Throughout most of the experiment, length and weight did not differ between the different photoperiod treatments, however whole body lipid and Fulton's condition factor did. Furthermore, changes in both whole body lipid and Fulton's condition factor in all treatment groups followed a similar seasonal pattern that was inversely related to day length (highest K and lipid levels found during days with the least light). These results suggest that regardless of age or size, there is a correlation between seasonal changes in photoperiod and changes in body composition in juvenile Chinook salmonids.

Evolution of tributary junctions and their capacity for rearing juvenile Chinook salmon (Oncorhynchus tshawytscha) on a regulated river

AbstractThe Trinity River in northern California was adjusting to unregulated flood and mining impacts when it was dammed and flow regulation began in 1960. We examine the subsequent evolution of the river's alluvial channel through 60 years of increases in regulated mainstem flow regimes in an unconfined and confined valley where Rush and Indian creeks respectively join the river 6.9 and 26.7 river kilometres from Lewiston Dam. The resulting capacity of the tributary junctions for rearing Chinook salmon fry in the current flow regime is evaluated with an empirical model developed for the Trinity River. Results indicate that morphologic changes at Indian Creek were relatively minor after damming because mainstem flows were restricted to a narrow channel in comparison to the channel at Rush Creek. Conversely, active channel and bar areas significantly declined at Rush Creek because the mainstem sediment supply was more severely reduced by flow regulation that enabled riparian vegetation to colonize the expansive alluvial surfaces that were present. These changes reduced instream habitat, suggesting salmon populations in large valleys may be at higher risk below dams than in smaller valleys where the reduced flow is confined to an already narrow channel. However, the relatively wide and unconfined valley responded more positively to increases in flow and sediment through the regulatory periods to yield significantly higher capacities for rearing Chinook fry. Therefore, while unconfined reaches may be particularly susceptible to change when a river is dammed, they may also provide the greatest opportunity for restoration of salmon populations.

Comparative Susceptibilities of Selected California Chinook Salmon and Steelhead Populations to Isolates of L Genogroup Infectious Hematopoietic Necrosis Virus (IHNV).

Simple SummaryChinook salmon in California conservation hatcheries have suffered disease outbreaks and significant mortality due to the fish virus infectious hematopoietic necrosis virus (IHNV) since at least the 1940s. Although steelhead trout in California are also occasionally infected with the same virus they do not typically experience disease. In this study the susceptibility of California Chinook salmon and steelhead trout was defined in controlled experiments that exposed groups of juvenile fish to California IHNV strains (L genogroup). The results confirmed high mortality among Chinook salmon but very low mortality of steelhead trout, despite identical virus exposures. Tests of varying conditions found increasing mortality of Chinook salmon with increasing virus dose, but reduced mortality at higher temperatures or with increased age or size of fish. Among Chinook salmon that survived virus exposure the persistence of virus was detected in one fish 8 months after virus exposure. These findings demonstrate that L genogroup IHNV in California has host specificity for Chinook salmon, and provide an understanding of factors that contribute to disease epidemics in California hatchery Chinook salmon.Salmonid species demonstrate varied susceptibility to the viral pathogen infectious hematopoietic necrosis virus (IHNV). In California conservation hatcheries, juvenile Chinook salmon (Oncorhynchus tshawytscha) have experienced disease outbreaks due to L genogroup IHNV since the 1940s, while indigenous steelhead (anadromous O. mykiss) appear relatively resistant. To characterize factors contributing to the losses of California salmonid fish due to IHNV, three populations of Chinook salmon and two populations of steelhead native to California watersheds were compared in controlled waterborne challenges with California L genogroup IHNV isolates at viral doses of 104–106 pfu mL−1. Chinook salmon fry were moderately to highly susceptible (CPM = 47–87%) when exposed to subgroup LI and LII IHNV. Susceptibility to mortality decreased with increasing age and also with a higher temperature. Mortality for steelhead fry exposed to two IHNV isolates was low (CPM = 1.3–33%). There was little intraspecies variation in susceptibility among populations of Chinook salmon and no differences in virulence between viruses strains. Viral persistence was demonstrated by the isolation of low levels of infectious IHNV from the skin of two juvenile Chinook salmon at 215 d post exposure. The persistence of the virus among Chinook salmon used for stocking into Lake Oroville may be an explanation for the severe epidemics of IHN at the Feather River hatchery in 1998–2002.

Damming salmon fry: evidence for predation by non‐native warmwater fishes in reservoirs

AbstractComplex predator–prey interactions over time have the potential to limit survival of threatened native species. Reservoirs created by large dams in temperate ecosystems are sites where both coldwater and warmwater fish species overlap in distributions, forming assemblages that would not occur under natural settings. For example, in many western North American reservoirs, juvenile native salmonids now overlap with native and non‐native predators such as Northern Pikeminnow Ptychocheilus oregonensis and bass Micropterus spp. Currently, native Northern Pikeminnow are considered by many to be the most formidable predator of salmon smolts in freshwater systems of the Pacific Northwest. However, their consumption of salmon fry and the role of non‐native warmwater predators remain unclear. Predation on fry has proved more difficult to identify than on smolts, due to smaller sizes and high digestibility, but is important for prioritizing management strategies. Here, we use multiple lines of evidence, including large datasets of stable isotopes and fish stomach contents, to identify which fish consume Chinook Salmon Oncorhynchus tshawytscha fry (<55 mm) as they enter reservoirs below their spawning grounds in the Middle Fork Willamette River, Oregon. Unexpectedly, we found that non‐native warmwater game fishes, including bass and crappie Pomoxis spp., preyed more heavily on Chinook Salmon fry in the spring than native fish predators including Northern Pikeminnow. Of the native species, only Rainbow Trout Oncorhynchus mykiss showed evidence for significant predation on Chinook Salmon fry. Fish management in reservoirs that attempts to promote both warmwater and coldwater recreational fisheries simultaneously may thus be in conflict, necessitating future prioritization of species composition in individual reservoirs. This prioritization is especially important as these species include popular game fishes as well as salmonids threatened under the U.S. Endangered Species Act. Understanding predation pressure by popular invasive game fishes on sensitive life stages will allow managers and policymakers to evaluate trade‐offs in the management of these novel assemblages.

Trophic Feasibility of Reintroducing Anadromous Salmonids in Three Reservoirs on the North Fork Lewis River, Washington: Prey Supply and Consumption Demand of Resident Fishes

AbstractThe reintroduction of anadromous salmonids in reservoirs is being proposed with increasing frequency, requiring baseline studies to evaluate feasibility and estimate the capacity of reservoir food webs to support reintroduced populations. Using three reservoirs on the north fork Lewis River as a case study, we demonstrate a method to determine juvenile salmonid smolt rearing capacities for lakes and reservoirs. To determine if the Lewis River reservoirs can support reintroduced populations of juvenile stream‐type Chinook Salmon Oncorhynchus tshawytscha, we evaluated the monthly production of daphnia Daphnia spp. (the primary zooplankton consumed by resident salmonids in the system) and used bioenergetics to model the consumption demand of resident fishes in each reservoir. To estimate the surplus of Daphnia prey available for reintroduced salmonids, we assumed a maximum sustainable exploitation rate and accounted for the consumption demand of resident fishes. The number of smolts that could have been supported was estimated by dividing any surplus Daphnia production by the simulated consumption demand of an individual Chinook Salmon fry rearing in the reservoir to successful smolt size. In all three reservoirs, densities of Daphnia were highest in the epilimnion, but warm epilimnetic temperatures and the vertical distribution of planktivores suggested that access to abundant epilimnetic prey was limited. By comparing accessible prey supply and demand on a monthly basis, we were able to identify potential prey supply bottlenecks that could limit smolt production and growth. These results demonstrate that a bioenergetics approach can be a valuable method of examining constraints on lake and reservoir rearing capacity, such as thermal structure and temporal food supply. This method enables numerical estimation of rearing capacity, which is a useful metric for managers evaluating the feasibility of reintroducing Pacific salmon Oncorhynchus spp. in lentic systems.Received April 24, 2016; accepted July 28, 2016 Published online October 11, 2016

Susceptibility of ocean- and stream-type Chinook salmon to isolates of the L, U, and M genogroups of infectious hematopoietic necrosis virus (IHNV).

This study examined the susceptibility of Chinook salmon Oncorhynchus tshawytscha to viral strains from the L, U, and M genogroups of infectious hematopoietic necrosis virus (IHNV) present in western North America. The goal of this investigation was to establish a baseline understanding of the susceptibility of ocean- and stream-type Chinook salmon to infection and mortality caused by exposure to commonly detected strains of L, U, and M IHNV. The L IHNV strain tested here was highly infectious and virulent in both Chinook salmon populations, following patterns previously reported for Chinook salmon. Furthermore, ocean- and stream-type Chinook salmon fry at 1 g can also become subclinically infected with U and M strains of IHNV without experiencing significant mortality. The stream-type life history phenotype was generally more susceptible to infection and suffered greater mortality than the ocean-type phenotype. Between the U and M genogroup strains tested, the U group strains were generally more infectious than the M group strains in both Chinook salmon types. Substantial viral clearance occurred by 30 d post exposure, but persistent viral infection was observed with L, U, and M strains in both host populations. While mortality decreased with increased host size in stream-type Chinook salmon, infection prevalence was not lower for all strains at a greater size. These results suggest that Chinook salmon may serve as reservoirs and/or vectors of U and M genogroup IHNV.

MODELLING CHANGES IN SALMON HABITAT ASSOCIATED WITH RIVER CHANNEL RESTORATION AND FLOW‐INDUCED CHANNEL ALTERATIONS

ABSTRACTThe River2D two‐dimensional hydraulic and habitat model was used to simulate fall‐run Chinook salmon (Oncorhynchus tschawytscha) spawning and fry and juvenile rearing habitat of the first phase of a stream channel restoration project on Clear Creek, California. Habitat was simulated for a range of stream flows: (1) before restoration; (2) based on the restoration design; (3) immediately after restoration; and (4) after one and two large flow events. Hydraulic and structural data were collected for three sites before restoration, and prerestoration habitat was simulated. Habitat simulated for these sites was extrapolated to the prerestoration area based on habitat mapping. The topographical plan for the restoration was used to simulate the anticipated habitat after restoration. Although the restoration increased spawning habitat, it was less successful for rearing habitat. Channel changes associated with high‐flow events did not entirely negate the benefits of the restoration project. The results of this study point out the need for models that can simulate the changes in channel topography associated with high‐flow events, which could then be used to simulate habitat over time. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

Parental Effect as a Primary Factor Limiting Egg‐to‐Fry Survival of Spring Chinook Salmon in the Upper Yakima River Basin

AbstractFew field estimates of egg‐to‐fry survival of Chinook salmon Oncorhynchus tshawytscha exist, although it is one of the major factors thought to limit freshwater production and recovery of Chinook salmon populations. This is likely due to the challenges of estimating survival at this life stage, which is further complicated by the variety of methods that have been employed. Our study objectives were to (1) develop a method by which spring Chinook salmon egg‐to‐fry survival could be estimated at a large spatial scale, and (2) investigate the primary factors affecting survival in the natural environment. We conducted a field experiment using 81 artificial redds to test our proposed method for evaluating egg‐to‐fry survival at a basin scale and to evaluate the effects of parentage (adult mating), river reach, and fine sediment infiltration on survival in the upper Yakima River basin, Washington. Egg‐to‐fry survival and preemergent Chinook salmon fry developmental stage were significantly different among matings, but were not detectably different among reaches. Fine sediment accumulation in egg boxes from artificial redds was largely below published threshold levels, explained less than 6% of the variation in survival, and was not correlated with developmental stage. In contrast, survival of individual matings in the natural environment and those same matings incubated under controlled hatchery conditions were highly correlated. Our study suggests that in years of low scour and potentially ideal incubation conditions, parental effects play an important role in determining in situ egg‐to‐fry survival, and that extensive replication and tracking of gamete viability is needed to separate parental effects from environmental factors affecting survival. We provide standardized methods for collecting egg‐to‐fry survival data and outline a number of potential biases that should be addressed in future research.

Calcein Mark Retention in Chinook Salmon and Steelhead Fry in Artificial and Natural Rearing Environments

AbstractHatchery Chinook salmon Oncorhynchus tshawytscha and steelhead O. mykiss fry were marked with calcein dye to determine its efficacy for identifying fish after release into the stream environment. The effects of the dye treatment on growth and survival of marked fish and the retention of the marks over time were evaluated in the presence and absence of sunlight. Minimal differences in growth were observed between marked and unmarked Chinook salmon, and there was no difference in the total length of marked and unmarked steelhead at the conclusion of the study. Calcein marking had no effect on survival of Chinook salmon or steelhead fry during the 8‐week experiment. The calcein mark rapidly lost its intensity over time in Chinook salmon and steelhead. Steelhead fry were marked and reared in three light treatments to directly evaluate whether sunlight exposure affected calcein retention. After 28 d, steelhead exposed to sunlight had no visible calcein marks, whereas those held in covered tanks had 100% mark retention. Chinook salmon fry were monitored in stream habitats after release into the stream environment. No marks were visible 8 months after release. These observations demonstrate reduced calcein mark retention in fish exposed to natural sunlight. Calcein mark retention differed between Chinook salmon and steelhead. Because externally visible calcein marks have a finite life span in the presence of sunlight, calcein use in long‐term fish‐marking projects will be limited.

Nearshore Areas Used by Fry Chinook Salmon, Oncorhynchus tshawytscha, in the Northwestern Sacramento-San Joaquin Delta, California

We report the geographic distribution and the densities and catch rates of Chinook salmon fry, Oncorhynchus tshawytscha, in different substrata and nearshore zones in the northwestern SacramentoSan Joaquin Delta of the San Francisco Estuary, California, USA. Nearshore zones in the freshwater, tidally influenced northwestern delta are dominated by riprap, and contain sparse sections of tule beds, beaches, and riparian zones. We sampled at six beach seine sites and eight electrofishing sites during winter 2001 along the Sacramento River,

Major histocompatibility complex heterozygote advantage and widespread bacterial infections in populations of Chinook salmon (Oncorhynchus tshawytscha)

Despite growing evidence for parasite-mediated selection on the vertebrate major histocompatibility complex (MHC), little is known about variation in the bacterial parasite community within and among host populations or its influence on MHC evolution. In this study, we characterize variation in the parasitic bacterial community associated with Chinook salmon (Oncorhynchus tshawytscha) fry in five populations in British Columbia (BC), Canada across 2 years, and examine whether bacterial infections are a potential source of selection on the MHC. We found an unprecedented diversity of bacteria infecting fry with a total of 55 unique bacteria identified. Bacterial infection rates varied from 9% to 29% among populations and there was a significant isolation by distance relationship in bacterial community phylogenetic similarity across the populations. Spatial variation in the frequency of infections and in the phylogenetic similarity of bacterial communities may result in differential parasite-mediated selection at the MHC across populations. Across all populations, we found evidence of a heterozygote advantage at the MHC class II, which may be a source of balancing selection on this locus. Interestingly, a co-inertia analysis indicated only susceptibility associations between a few of the MHC class I and II alleles and specific bacterial parasites; there was no evidence that any of the alleles provided resistance to the bacteria. Our results reveal a complex bacterial community infecting populations of a fish and underscore the importance of considering the role of multiple pathogens in the evolution of host adaptations.

Salmonid Fry Stranding Mortality Associated with Daily Water Level Fluctuations in Trail Bridge Reservoir, Oregon

AbstractLittle information exists on how reservoir fluctuations affect stranding risk for early life stages of salmonids. This study focuses on the effects of hydroelectric‐related water level fluctuations in Trail Bridge Reservoir, Oregon, where salmonids, including the bull trout Salvelinus confluentus and spring Chinook salmon Oncorhynchus tshawytscha, which are listed under the U.S. Endangered Species Act, commonly occur. A distance‐from‐line sampling design was employed using permanently established transects to estimate the magnitude of stranding of juvenile salmonids during 30 surveys over 3 months in spring 2006. All stranded fish observed during field surveys were mapped onto spatially rectified, low‐elevation aerial photographs to assess the patterns in stranding. Most fish were stranded in habitats with a slope of less than 6%, typically in interstitial spaces among cobbles, and in “potholes.” Fish were stranded in similar numbers following small or large fluctuations, and no relationship was apparent between the range in fluctuation and the number of stranded fish or between the average rate of water surface decline and the number of stranded fish. Based on extrapolation, we estimated that 808 spring Chinook salmon fry and 444 brook trout S. fontinalis fry were stranded in Trail Bridge Reservoir during spring 2006. One dead bull trout was observed, but based on the abrasions, open wounds, and signs of infection that we observed, it died prior to the decline in reservoir elevation. Our findings suggest that stranding in this reservoir could be reduced (while retaining the hydroelectric function of the reservoir) by restricting fluctuations to specific elevations during vulnerable fish migration periods, increasing the slope of areas identified as having a high stranding risk, or both.

The effects of domestication on the relative vulnerability of hatchery and wild origin spring Chinook salmon (Oncorhynchus tshawytscha) to predation

We tested whether one generation of state-of-the-art hatchery culture influenced the vulnerability of Chinook salmon (Oncorhynchus tshawytscha) fry to predators. Size-matched hatchery and wild origin spring Chinook salmon fry were exposed to rainbow trout (Oncorhynchus mykiss) and torrent sculpin (Cottus rhotheus) predators in 10.8 m3 net pens. The hatchery origin fry were the offspring of first generation hatchery-reared broodstock, and the wild origin fry had no history of hatchery culture; both originated from the same stock. Wild origin fry were found to have a 2.2% (p = 0.016) survival advantage over hatchery origin fry during 2 years of predation challenges. The most important findings of this study are (i) domestication can affect the susceptibility to predators after only one generation of state-of-the-art hatchery culture practices, and (ii) the domestication effect was very small.

Survival, Development, and Growth of Fall Chinook Salmon Embryos, Alevins, and Fry Exposed to Variable Thermal and Dissolved Oxygen Regimes

AbstractSome fall Chinook salmon Oncorhynchus tshawytscha initiate spawning in the Snake River downstream of Hells Canyon Dam at temperatures that exceed 13°C and at intergravel dissolved oxygen concentrations that are less than 8 mg O2/L. Although water temperature declines and dissolved oxygen increases soon after spawning, the initial temperature and dissolved oxygen levels do not meet the water quality standards established by the states of Oregon and Idaho for salmonid spawning. Our objective was to determine whether temperatures from 13°C to 17°C and dissolved oxygen levels from 4 to more than 8 mg O2/L during the first 40 d of incubation followed by declining temperature and rising dissolved oxygen affected survival, development, and growth of Snake River fall Chinook salmon embryos, alevins, and fry. During the first 40 d of incubation, temperatures were experimentally adjusted downward approximately 0.2°C/d and oxygen was increased in increments of 2 mg O2/L to mimic the thermal and oxygen regime of the Snake River where these fish spawn. At 40 d postfertilization, embryos were moved to a common exposure regime that followed the thermal and dissolved oxygen profile of the Snake River through emergence. Mortality of fall Chinook salmon embryos increased markedly at initial incubation temperatures of 17°C or more, and a rapid decline in survival occurred between 16.5°C and 17°C; there were no significant differences in survival at temperatures up to 16.5°C. Initial dissolved oxygen levels as low as 4 mg O2/L over a range of initial temperatures from 15°C to 16.5°C did not affect embryo survival to emergence. There were no significant differences in alevin and fry size at hatch and emergence across the range of initial temperature exposures. The number of days from fertilization to eyed egg, hatch, and emergence was highly related to temperature and dissolved oxygen; fish required from 6 to 10 d longer to reach hatch at 4 mg O2/L than at saturation and up to 24 d longer to reach emergence. In contrast, within each dissolved oxygen treatment, fish required about 20 d longer to reach hatch at 13°C than at 16.5°C (no data were available for 17°C) and up to 41 d longer to reach emergence. Overall, this study indicates that exposure to water temperatures up to 16.5°C will not have deleterious effects on survival or growth from egg to emergence if temperatures decline at a rate of 0.2°C/d or more after spawning. Although fall Chinook salmon survived low initial dissolved oxygen levels, the delay in emergence could have significant long‐term effects on their survival. Thus, an exemption to the state water quality standards for temperature—but not oxygen—may be warranted for the portions of the Snake River where fall Chinook salmon spawn.

Modeling changes in salmon spawning and rearing habitat associated with river channel restoration1

The River2D two‐dimensional hydraulic and habitat model was used to simulate fall‐run chinook salmon (Oncorhynchus tschawytscha) spawning and fry and juvenile rearing habitat before and after restoration of stream channel sites for a range of streamflows on the Merced River and Clear Creek, California. For the Merced River, hydraulic and structural data were collected for four sites before and after restoration, representing all habitat types within the restoration reach. Habitat simulated for these sites was extrapolated to the entire restoration reach based on habitat mapping. For Clear Creek, hydraulic and structural data were collected for four sites before restoration and pre‐restoration habitat was simulated. The topographic plan for the restoration was used to simulate habitat after restoration. While the restoration generally increased spawning habitat, it was less successful for rearing habitat. The results of this modeling show how they can be used in a cost‐effective adaptive management framework to evaluate restoration project design prior to construction.

A Classification of Habitat Types in a Large River and Their Use by Juvenile Salmonids

AbstractWe describe six habitat types for large rivers (>100 m bank‐full width), including pools, riffles, and glides in midchannel and bank edges, bar edges, and backwaters along channel margins. Midchannel units were deeper and faster than edge units on average. Among edge habitat types, backwater units had the lowest velocities and contained complex cover consisting mainly of wood accumulations and aquatic plants. Banks and bars had similar velocity distributions, but banks had more complex cover such as rootwads and debris jams. Because sampling of juvenile salmonids was ineffective in the midchannel units (electrofishing capture efficiency was low, and the units were too deep and fast to snorkel), we focused our sampling efforts on juvenile salmonid use of edge habitats during winter, spring, and late summer. Densities of juvenile Chinook salmon Oncorhynchus tshawytscha and coho salmon O. kisutch were highest in bank and backwater units in winter, whereas age‐0 and age‐1 or older steelhead densities were highest in bank units in winter. In summer, only coho salmon densities were significantly different among edge unit types, densities being highest in banks and backwaters. Microhabitat selection (velocity, depth, and cover type) by juvenile salmonids mirrored that in small streams, most fish occupying areas with a velocity less than 15 cm/s and wood cover. Among ocean‐type salmon, Chinook and chum salmon fry were captured in large numbers in all edge units and exhibited only slightly higher densities in low‐velocity areas (<15 cm/s).

Recruitment and distribution of juvenile salmonids in Lake Coleridge, New Zealand

Rainbow trout (Oncorhynchus mykiss Richardson) and chinook salmon (O. tshawytscha Walbaum) fry and 0+ fingerlings entered Lake Coleridge, a deep, oligotrophic lake in the Southern Alps of New Zealand, in spring and early summer and dispersed throughout the shallow littoral. In contrast, most juvenile brown trout (Salmo trutta Linnaeus) remained in the tributaries for 1–2 years before migrating down stream to the lake. Juvenile salmonids (<35Omm) were more abundant in the shallow littoral (<10 m), especially near tributaries, than in the deep littoral (10–40 m), or the surface layers (0–16 m) of the limnetic zone which were populated by yearling (>150 mm) and adult salmon and rainbow trout (>210 mm). The abundance of 0+ rainbow trout in the littoral zone declined rapidly from February to August and stocks were supplemented by a migration of yearling fish from the tributaries in spring. The shallow littoral zone and tributaries are both important for juvenile trout rearing in this lake.

Control of growth and adiposity of juvenile chinook salmon ( Oncorhynchus tshawytscha)

Chinook salmon fry (0.7 g, 3.9% whole body lipid) were fed high protein diets containing high lipid (HL) (65% protein, 23% lipid) or low lipid (LL) (85% protein, 3% lipid) at high ration (near satiation = HR) or low ration (one half of high ration = LR) for 247 days to determine if growth and adiposity could be independently controlled. Each treatment was duplicated with each tank containing 400 fish. The amount of feed fed to each tank of fish was adjusted each month so that fish fed at a prescribed ration level (HR or LR) would grow at similar rates. The effects of ration and dietary lipid level on final weight, adiposity, feed efficiency (wet weight gain/dry feed fed) and protein retention efficiency were assessed using regression, two-way ANOVA and ANCOVA ( P < 0.05). Overall feed efficiency (109–127%) was lowest in the HR/HL treatment but differences among treatments were not significant. For the different treatments (HR/HL, HR/LL, LR/HL, LR/LL), the amounts of dry feed fed averaged; 17.5, 15.4, 6.7 and 6.1 g/fish, final mean fish weights were, 20.2, 19.5, 9.2 and 8.7 g and final mean whole body lipids were, 11.3, 5.4, 7.1, 3.9%. These results show that ration level had the major influence on growth, whereas dietary lipid level was the major determinant of adiposity. This appears to have occurred because when protein was supplied in excess, it was not spared by lipid. Thus it may be possible for enhancement hatcheries and commercial salmon farms to manipulate growth and adiposity by regulating ration and controlling diet composition.

Created and Restored Marshes in the Lower Fraser River, British Columbia: Summary of their Functioning as Fish Habitat

Abstract Ecological comparisons of transplanted, natural (reference) and disrupted (unvegetated) marsh sites on the Fraser River estuary, British Columbia, were conducted between 1991 and 1994. The study examined vegetative biomass and cover, invertebrate abundance, fish abundance, fish residency, fish food, and submergence time for the three habitats. Standing crop biomass at three transplant sites was within the range of values for reference sites, but was much lower at an unstable site where sediment slumping had occurred. The percent cover of Lyngbyei's sedge (Carex lyngbyei) in eight transplant sites was 0.05) was observed among marsh sites when chum salmon (Oncorhynchus keta) and chinook salmon (O. tschawytscha) fry abundance were compared. However, chinook and sockeye smolt catches were significantly different (p&amp;gt;0.05) was observed among marsh sites when chum salmon (Oncorhynchus keta) and chinook salmon (O. tschawytscha) fry abundance were compared. However, chinook and sockeye smolt catches were significantly different (p&amp;lt;0.05) among marsh sites and were usually higher at disrupted sites. In nine sites in the North Arm and Deas Slough area chum fry residency was examined. At one transplant site (DEI) marked chum fry were caught up to 48 h after release. No fry were caught 1 h after release at a transplant site (Dll) and a disrupted site (DE4). At the remaining sites, fry were caught up to 1 and 3 h after release. At all sites, over 80% of the total number of food organisms examined in chum fry stomachs were harpacticoid copepods. Mean submergence time for reference marshes ranged from 33.2 to 50.7%, but for transplanted sites the value ranged from 26.4 to 60.1%. Our study shows that numerous factors need to be examined in determining if restored marshes will function as natural habitats. The development of a standardized set of reference criteria would assist in evaluating whether or not transplanted marshes are functioning as designed.